My current problem is knowing the best way to control the 7 and maybe more fans that I will be controlling. This fans are currently set in 5 groups or channels based on location and purpose in the case so. I want to be able to set them manually and also set them programmatically.
I question the need to control the fans independently... i.e. It wouldn't make sense to have some fans running full-speed and others off.
I want to control the speed of the fans individually because I don't need them running full speed during about 8 months of the year where the temperatures are very pleasant where I live. However, during the summer months, even with the air-conditioner running, it can get very hot. The fans, despite being very quiet fans, get really loud when blowing through the radiator. These are the two fans that I need the most granular control over anyway, but there are times I need to control the others too.
So I was thinking that the best way to do that would be to have a slide pot for manual input
That would be OK. But it's mechanically easier to drill a round hole and mount a rotary pot. Another option would be to have buttons for "faster" and "slower". And, with an LCD you have the option of "soft buttons" where a button can have one or more functions, controlled by software.
Reason for slidepot is the location that the "quick control" would be which is in the included picture with SD card for scale.
It's better to use PWM to a MOSFET. You wouldn't need the digital pots and you already have PWM outputs. Linearly controlling the voltage/speed with a pot (or digital pot) is inefficient and it requires the MOSFET to dissipate heat.
This is because MOSFETs switching speed is very quick and allowing them be be fully open ensures low heat created/dissipated, correct? And here was another one of my questions... PWM on these fans will work despite the fact that they aren't "PWM compatible" PC fans? They just have the 3 pins VCC, GRD, and the sensor which I believe gives a square wave with a peak at each full revolution.
If PWM works, then that makes the project much easier as a PWM to a MOSFET would be much to implement as well as much cheaper.
